Summary of the geotechnical and structural problems of the I-495 Bridge
The I-495 Bridge in Wilmington, Delaware experienced geotechnical and structural problems leading to its closure. According to structural engineers, the closure of the bridge was following an external force that caused the four pillars of the bridge to tilt. The 11-mile long bypass through the bridge remains closed for an unknown time. The tilting pillars were because of a shifting force on the earth surface, but the engineers had not yet identified the source. Engineers and workers are using shovels, and high-powered sensors to discover the main cause of the shifts on the ground (Nann, and Jeff 1).
After exclusive analysis, geotechnical experts conclude that the shifting forces on the bridge are consistent with the forces from seismic activities, or extensive weight of a colossal dirt pile compressing soils towards the leaning piers. An earthquake remains a probable cause of the damage of the bridge even if no signs of a seismic event. However, corrosion was ruled out as a probable cause of the tilting of the pillars after extensive research on it as a cause of the shifting force. There are allegations that the bridge cannot withstand full traffic load despite its ability to support its weight. The bridge remains closed until its reconstruction with consideration of the probable causes of reoccurrence of a similar problem (Nann, and Jeff 1).
According to the USArray seismic network, the magnitude 6.0 Earthquake Near American Canyon occurred on Sunday August 24, 2014 at 3:20 AM (PDT). The earthquake had a depth focus was approximately 11 KM and lied within approximately 70 km width of major faults of the San Andreas Fault system. The distance between the epicenter and the closest recording station is approximately 222 km. The epicenter of the earthquake is the Napa region (USGS 1).
The earthquake exists within a 44 miles set of main faults of the San Andreas Fault system that define the boundary between the Pacific and North American tectonic plates. The importunate northwestward movement of the Pacific plate to North America mainly causes right-lateral slip across key faults and defines deformation between the main faults (USGS 1).
The earthquake occurred between two large strike-slip fault systems. The Hayward-Rodgers Creek Fault system, which is nearly 4 miles west of the site, may have been a major force towards the occurrence of the earthquakes. The fault system was responsible for earthquakes in 1868. Also, the Concord-Green Valley Fault system, which is approximately 7 miles east of the Napa could have been responsible for the earthquake (USGS 1).
The earthquake took place close to the North shore of San Pablo Bay. The region is underlain by landfill and bay mud, which led to disproportional damage of historic earthquakes. The extensive damage is because of soil failure in the fills, as well as amplification of shaking of the ground from the soft bay mud (USGS 1).
Comparison with the Sumatran earthquake and Great East Japan earthquake
The 9.0 earthquake in Japan also known as Great East Japan earthquake, with an epicenter nearly 80 miles east of Sendai, generated a tsunami that got to a height of approximately 132 feet. The earthquake travelled up to approximately 6 miles inland. Unlike the American Canyon earthquake, the Great East Japan the epicenter was approximately 43 miles east of the Oshika Peninsula of Tohoku (VUME 1). However, the two earthquakes share the science of earthquakes. They depend on the effects of the crust and upper mantle, referred to as lithosphere. The earthquakes were following existence of extensive forces on the ground that triggered the stability of the land. Unlike the American Canyon earthquake, the Great East Japan earthquake was mainly affected by the Philippine faults (VUME 1).The two earthquakes were equally disastrous as they caused extensive loss to the land. There were major movements on the ground that led to the earthquakes. However, the three earthquakes varied on strength and the epicenters.
The giant Sumatra earthquake that occurred in 2004 recorded the greatest fault length of any previous earthquake, covering a distance of approximately 900 miles. Like the American Canyon, the giant Sumatra earthquake started from an epicenter. However, there are differences between the two earthquakes (Tectonics Observatory 1). The section of the fault that ruptured is found deep in the earth’s crust, in regions as much as 31 miles below the ocean floor. The earthquake was because of two tectonic plates, which were stuck together, and suddenly broke free with the upper plate sliding back upwards, as well as to the west by approximately 65 feet along the boundary of the plate. The Sumatra earthquake had extensive impact on the oceans while the American Canyon was mainly influential to the land. The rupture propagation made the ocean floor to spring back to the west by approximately 20 feet, and uplift by approximately 6 feet (Tectonics Observatory 1). The displacement of the ocean floor was sudden and shoved the water upwards. The gigantic push of the water caused a series of tsunami waves with the waves growing to approximately 100 feet high in some places (Tectonics Observatory 1).
Works Cited
Nann Burke , Melissa , and Jeff Montgomery. "Cracks found in I-495 bridge in Delaware." Cracks found in I-495 bridge in Delaware. N.p., n.d. Web. 4 Sept. 2014. http://www.delawareonline.com/story/news/traffic/2014/06/05/markell-weeks-months-reopens-delaware/10032061/.
Tectonics Observatory . "2004 Sumatra Earthquake." 2004 Sumatra Earthquake. N.p., n.d. Web. 3 Sept. 2014. <http://www.tectonics.caltech.edu/outreach/highlights/sumatra/what.html>.
USGS. "M6.0 - 6km NW of American Canyon, California 2014-08-24 10:20:44 UTC." M6.0 - 6km NW of American Canyon, California 2014-08-24 10:20:44 UTC. N.p., n.d. Web. 1 Sept. 2014. <http://earthquake.usgs.gov/earthquakes/eventpage/nc72282711#summary>.
VUME. "2011 Sendai earthquake and tsunami | Japan earthquake." 2011 Sendai earthquake and tsunami | Japan earthquake. N.p., n.d. Web. 4 Sept. 2014. <http://www.virtualuppermantle.info/2011-Sendai-Japan.htm>.
Appendix
Seismogram for the American Canyon
The x-axis indicates the ground motion while the y-axis measures the time of occurrence.
UTC (Coordinated Universal Time) refers to the primary standard time by which the global clocks and time are regulated. The Pacific Time was used in this seismogram.
American Canyon Map
The 2004 Sumatra Earthquake Map
Great East Japan (Sendai) earthquake Map
